old fashioned home thermostat Honeywell CT87B Round


I replaced an old Honeywell Round with a new Honeywell Round CT87B. Now the fan won't come on with the heat when fan is set on auto.

Any help?

Matt Whitlock
Matt Whitlock's picture


I'm certainly not the most qualified person to answer heating/cooling questions, but I'll help if I can.

Is the connection to your furnace a 3, 4, or 5 wire connection?

Madd Max
Madd Max's picture
I had to hire in an

I had to hire in an electrical engineer for 5 hours yesterday to trouble-shoot my solar heat collection system in conjunction with a gas fired backup which the blower was running continiously... my brother had replaced the TOP of a Honeywell CT87A base...and have 4 wires from the system. Consequently, the top piece doesn't use the green wire (Lookup Honeywell website-thermostats-ct87A! Look at page 8 of the schematics which lists which wires work on which model...) and made the gas run ANYTIME the house called for heat, even if the solar system had the heat available- resulting in a gas bill of $492 and an electrical bill of $495 last month!


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